Grain size controls on cryoturbation and soil organic carbon density in permafrost-affected soils

This meta-analysis aims to describe the relationship between grain size distributions and soil organic carbon (SOC) storage in mineral subsoil and SOC-enriched cryoturbated pockets in five areas of continuous permafrost that differ in glaciation history and soil parent materials. Our results show a positive relationship between the proportion of soil particles in fine-grained fractions (colloid to medium silt) and SOC storage. Finer textured soils had significantly higher SOC storage in mineral subsoil samples (not SOC-enriched through cryoturbation) than coarser textured soils. However, the process of SOC enrichment through cryoturbation was most pronounced in soils with coarser grain sizes in the range of coarse silt and very fine sand. Although fine-grained textures provide better physical and biochemical protection for soil organic matter, their strong cohesion reduces the mixing of soil horizons and the effectiveness of cryoturbation. A higher ratio of coarse silt to clay in samples was a good predictor of SOC enrichment through cryoturbation across soil samples, soil profiles and study areas.